# Rotational mechanical systems and electrical analogs.

1. Nov 11, 2013

### peripatein

Hi,
1. The problem statement, all variables and given/known data
Upon converting rotational mechanical components into their electrical analogs, one thing in particular baffles me. When is a rotational component converted into two sets of dependent sources and when is it converted into a single set? Let me try and clarify my question via a few examples.
In attachment 1, the pulley is converted into two sets of dependent sources: the first (v=ωR; τ2=F2R) is, I guess, the analog of the torque created by the rope pulled by F2, whereas the second (ω=v1/R; F11/R) is, I guess, the analog of the moment of inertia itself.
However, in attachment 2, a single set of dependent sources is used in the conversion. Why? What about the torque created by the pull of the rope? There seems to be some sort of discrepancy between the rationale behind this example and the one governing the first.
In attachment 3, J is converted into its analog - so far so good, but what about the force exerted by the strip which is under the wheel and which surely creates a torque?
Attachment 4 again shows no evidence of the supposedly expected analog of the torque created by the rope. Why?
Furthermore, why is Bs in attachment 4 in series whereas B1 in attachment 3 is in parallel?
I'd sincerely appreciate some explanations on these delicate points.

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